Page 715 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

702 SPECIAL THERAPY

urea concentrations will underestimate true dialysis dose ultrafiltration requirements, and the intensity of dialy-
because of a failure to account for the convective sis. 122 Chronic hyperkalemia often is difficult to manage
contributions. 48 and poses a persistent and life-threatening risk. The
causes remain unknown but likely involve dialysis-
USE OF HEMODIALYSIS TO CORRECT induced disruptions of cell potassium or cell volume reg-
ELECTROLYTE IMBALANCES ulation, excesses in dietary potassium load, or altered
Uremic animals experience a wide spectrum of electrolyte potassium regulation associated with severe chronic
imbalances because the kidneys are responsible for uremia. The use of a dialysate containing 0 mmol/L of
homeostatic regulation of body electrolytes. potassium decreased the prevalence of hyperkalemia at
Hyperkalemia is the most common and life-threatening future dialysis sessions by 50% compared with a standard
electrolyte imbalance encountered in animals with either dialysate containing 3.0 mmol/L potassium. Use of a
acute or chronic uremia and can cause severe cardiovascu- standard dialysate may actually increase the prevalence
lar instability and death. The toxicity of potassium is for severe hyperkalemia (serum potassium >7.0 mmol/L).
intensified by acidosis, hypocalcemia, and hyponatremia More recently, evidence in dogs with chronic kidney
that may coexist with uremia. Hyperkalemia is a consistent disease suggests hyperkalemia can be induced directly
complication of acute uremia intensifying with the severity by the use of therapeutic renal diets commonly fed to dogs
of the azotemia and presence of oligoanuria. 35,36,95 with CKD and dogs undergoing maintenance dialysis. 149
Predialysis hyperkalemia has been recognized with These observations support a role for an excessive dietary
increased frequency in dogs maintained on hemodialysis potassium load rather than causal effects of the dialysis
for greater than 2 weeks. 122 Preliminary findings prescription. 149
demonstrated 20 of 27 dogs (74%) undergoing dialyzed Life-threatening electrocardiographic abnormalities
for longer than 2 weeks had episodes of predialysis resulting from hyperkalemia may be reversed completely
hyperkalemia associated with approximately 50% of 544 within minutes of initiating hemodialysis using a dialysate
hemodialysis sessions. The hyperkalemia ranged in sever- containing 0 mmol/L of potassium (Figure 29-11). The
ity between 6 and 10 mmol/L and may be associated mechanism for the immediate effect is not known but is
with varying degrees of hyponatremia, hypercalcemia, disassociated from improvements in serum potassium
and metabolic acidosis. Its prevalence is associated with concentration, which remains unchanged at this stage
the duration of dialytic support, degree of azotemia, of the treatment. Consequently, for dialysis sessions in

Figure 29-11 A, Predialysis electrocardiogram (ECG) from a uremic dog with a serum potassium
concentration of 9.6 mmol/L and evident cardiotoxicity. B, ECG from the same animal within 15 minutes of
starting hemodialysis with a 0 mmol/L potassium dialysate. The improvement in the ECG was independent of
changes in the peripheral potassium concentration.